The present specification generally relates to mobile radio communications with focus on Self-optimizing Networks (SON) and in particular to Coverage and Capacity Optimization (CCO) use case and mechanisms.
Coverage holes are one of network issues causing Radio Link Failures (RLF) and call drops, and CCO is the SON use case to cope with these issues.
In mobile radio communications, different types of coverage holes exist. There are concepts of RLF reporting and analysis which provide means to identify coverage holes and separate them from mobility related failures.
However, in order to allow an efficient CCO algorithm, a more detailed analysis of the root cause of a coverage hole than with the above mentioned concepts is needed. Namely, only with detailed knowledge regarding a root cause of a coverage hole, the appropriate countermeasures might be determined.
Here, coverage holes with unbalanced uplink (UL) and downlink (DL) require particular consideration. FIG. 6 illustrates such coverage holes (in particular an UL coverage hole) with unbalanced UL and DL. In particular, according to FIG. 6, DL coverages of two cells are indicated by solid lines, while UL coverages of these two cells are indicated by dotted lines. As can be seen, in such possible scenario, a mobile device might be inside a DL coverage area of a cell while the same mobile device is outside the UL coverage area of that cell, i.e., in a coverage hole.
Often when mobile terminals are in a coverage hole situation, the UL connection is lost while DL connection is still good. When such a terminal experiences a RLF, the terminal tries to re-establish or re-connect to the network since the received DL signal still indicates good coverage. But both re-establishment and re-connection will fail since the UL is not working. Later, when also UL connection becomes stable again, the terminal is able to re-connect, and a RLF report sent by the terminal can be analysed at the network.
According to existing concepts, an RLF report represents the situation at the moment the RLF occurred.
According to a further concept, a Connection Establishment Failure (CEF) report contains information regarding the last failed connection setup.
According to a further concept, Minimization of Drive Tests (MDT) idle mode logging is specified. Here, the network can instruct the UEs to log measurements even when they are not in connected mode.
Considering the outlined known concepts, rather sparse information related to an occurred coverage hole is available, such that the problem arises that relevant information beneficial for coverage hole analysis and detection is not provided to the network.
Hence, there is a need to provide for improvement of coverage hole analysis.